let fooExports = require('./foo.js');// 用一个变量接收 foo.js向外暴露的成员
let foo2Exports = require('./foo2.js');

// console.log(foo); // ReferenceError: foo is not defined

console.log(fooExports); // { add: [Function: add], str: 'Hello' }
console.log(foo2Exports);// hello

